Conventional facilities for reducing NOx in exhaust gas from combustion engines employ methods such as the selective catalytic reduction (SCR) method and the selective non-catalytic reduction (SNCR) method. In the SCR method, a reducing agent is sprayed into the exhaust gas, and the exhaust gas is denitrated with a catalyst. The SNCR method accomplishes denitration without using a catalyst.
Among transport machines employing the SCR method for example, cars traveling on land by a diesel engine can be replenished with a reducing agent such as ammonia water (NH3) and urea water at a large number of sites. Therefore, such cars can be replenished with a reducing agent immediately when running out of the reducing agent while traveling. By contrast, ships among the above transport machines generate a larger amount of exhaust gas and thus require a larger amount of reducing agent than the cars, and moreover, ships can only be replenished with the reducing agent when visiting a port. Therefore, reducing agents having a smaller volume, such as urea powder, are studied for use in SCR for the ships.
For example, Patent Literature 1 discloses an exhaust gas purifying system that uses urea powder loaded on a ship. This system uses a fresh water generator, serving as one of the ship facilities, to generate urea water from the urea powder at any time. A ship that cannot be replenished with urea water at sea can be equipped with this exhaust gas purifying system to purify an exhaust gas (reduce the amount of NOx in the exhaust gas) while reducing the required space and the burden of the ship.